Distance measurement equipment is a navigation technology that provides information about the distance between an airborne vehicle and a control tower at an airport. Typically distance measurement equipment is used by a pilot while landing the airborne vehicle. The distance measurement equipment in the airborne vehicle determines propagation delay of ultra-high frequency (UHF) radio signals in order to provide the distance information.
The analog-to-digital converters currently available for use in the distance measurement equipment have limited sample rates. The effective number of bits of resolution of the current analog-to-digital converters is also limited. These limitations have a deleterious impact on the performance of distance measurement equipment (DME), which needs to capture and detect signals in a wide frequency bandwidth. When the analog-to-digital converter in the distance measurement equipment system has enough bits of resolution, the analog-to-digital converter sample rate is too low to capture the entire range of DME channels without some DME channels aliasing onto other channels after the sampling process. Likewise, analog mixer images can be aliased as undesired signals on the desired channel. If aliasing occurs, undesired signal falls on a desired channel and reception on the desired channel is degraded. To overcome aliasing effects, complex RF filters are required.